Chronic lymphocytic leukemia (CLL) originates from B lymphocytes which differ in activation and maturation stage and are derived from antigen experienced B cells with different immunoglobulin heavy chain variable (IgVH) gene mutations (Chiorazzi N et al., N. Engl. J. Med., 2005, 352, 804-15). Patients with mutated IgVH genes have a better prognosis compared to patients with unmutated genes (Damle R N et al., Blood 1999, 94, 1840-7; Hamblin T J et al., Blood, 1999, 94, 1848-54). Global gene expression profiling studies have revealed partly distinguishing but in general overlapping expression profiles in mutated and unmutated leukemic B cells, suggesting a common phenotype (Klein U et al., J. Exp. Med., 2001, 194, 1625-38; Rosenwald A et al., J. Exp. Med., 2001, 194, 1639-47).
Gene expression profiling studies showed a 43.8 fold increase of the orphan receptor tyrosine kinase (RTK) ROR1 in CLL cells (Klein U et al., J. Exp. Med., 2001, 194, 1625-38). ROR1 is a member of the RTK family of orphan receptors related to muscle specific kinase (MUSK) and Trk neurotrophin receptors (Glass D J, et al., Cell, 1996, 85, 513-23; Masiakowski P et al., J. Biol. Chem., 1992, 267, 26181-90; Valenzuela D M et al., Neuron, 1995, 15, 573-84). ROR receptors are cell surface receptors participating in signal transduction, cell-cell interaction, regulation of cell proliferation, differentiation, cell metabolism and survival (Masiakowski P et al., Biol. Chem., 1992, 267, 26181-90; Yoda A et al., J. Recept. Signal Transduct. Res., 2003, 23, 1-15). They are evolutionarily highly conserved between different species e. g. human, mouse, Drosophila, and C. elegans, suggesting important biological functions.
The human ROR1 gene has a coding region of 2814 bp with a predicted 937 amino acids sequence and 105 kDa protein size including an Ig-like domain, cysteine-rich domain, kringle domain, tyrosine kinase domain, and proline-rich domain (Yoda A et al., J. Recept. Signal Transduct. Res., 2003, 23, 1-15). ROR1 is located on chromosomal region 1p31.3 (http://www.ensembl.org), a region where chromosomal aberrations are not frequently seen in hematological malignancies. The human ROR1 is expressed at the gene level in heart, lung, and kidney but less in placenta, pancreas and skeletal muscles (Reddy U R et al., Oncogene, 1996, 13, 1555-9). Importantly, there is an almost complete absence of ROR1 protein expression in normal human adult tissues and organs. ROR1 was originally cloned from a neuroblastoma cell line (Masiakowski P et al., J. Biol. Chem., 1992, 267, 26181-90) and subsequently a shorter form lacking the entire extracellular domain but containing the transmembrane domain was isolated from a fetal brain library. Truncated ROR1 (t-Ror1) gene has been reported in fetal and adult human central nervous system, in human leukemias, lymphoma cell lines, and in a variety of human cancers derived from neuroectoderm (Reddy U R et al., Oncogene, 1996, 13, 1555-9). A shorter transcript from exons 1-7 including a short part of intron 7 has also been described with a predicted length of 393 amino acids and a molecular weight of 44 kDa (Ensembl ID; ENSG00000185483).
Gene profiling and protein expression studies of patients with chronic lymphocytic leukemia (CLL) has revealed increased expression of ROR1, while mature leucocytes from healthy donors do not express this protein (DaneshManesh, A H et al., Int. J. Cancer, 2008, 123, 1190-5). Silencing of ROR1 with siRNA in CLL cells resulted in apoptosis, while siRNA treatment of B cells from normal donors did not (Choudhury, A et al., Brit. J. Haematol., 2010, 151, 327-35).
Acute myeloid leukemic (AML) stem cells (CD34+) may potentially account for the resistance for many cytotoxic drugs. In an in vitro assay, a chimeric antibody against ROR1 (UC99961) inhibited in a dose-dependent manner colony formation of ROR1+ AML stem cells but not ROR− AML cells and not normal CD34+ stem cells. The results suggest that targeting ROR may represent an important component to eradicate malignant stem cells in AML and potentially also other refractory cancer-stem-cell-driven malignancies (Balaian L et al, Blood, ASH Annual Meeting) 2012, Abstract 2560). In acute lymphoblastic leukemia (ALL) ROR1 is up-regulated modulating in a counterbalancing manner with pre-BCR signaling pathways leading to activation of AKT, ERK and MEK. siRNA transfection induced impaired growth of ALL cells and apoptosis (Bicocca V et al, Cancer Cell, 22, 656-667, 2012).
Human breast cancer cells, but not normal breast epithelia cells also express ROR1. The intensity of ROR1 expression was higher in patients with hormone receptor negative tumors as well as in those with a low degree of cell differentiation, i.e. in patients with a poor prognosis. Silencing of ROR1 impaired the growth in vitro of human breast cancer cells and in immune-deficient mice. The results support the notion that ROR1 is of biological and clinical significance in breast cancer and may be a potential target for therapy (Zang S et al, PLoS One, 7(3): e31127, 2012).
In human lung adenocarcinoma cells ROR1 was overexpressed. The ROR1 kinase activity sustained a favorable prosurvival balance between the proliferative PI3K/AKT and apoptotic p38 signaling, partly through ROR1 kinase-dependent src activation as well as kinase-independent sustainment of EGFR/ERBB3 phosphorylation and PI3K activation. ROR1 knock-down effectively inhibited the growth of lung cancer cells in vitro and in vivo irrespective of EGFR status including those cells resistant to the EGFR tyrosine kinase inhibitor gefitinib. These data also indicate an important biological role of ROR1 in lung cancer and a structure for targeted therapy (Yamaguchi et al, Cancer Cell, 21, 348-361, 2012). Unexpectedly CLL cells showed an overexpression of ERBB2 and phosphorylation of src/PI3K, AKT/mTOR/CREB. The ROR1 tyrosine kinase inhibitors described in this work (see below) dephosphorylated ROR1/src/PI3K/AKT/mTOR/CREB which preceded apoptosis of CLL cells (own unpublished observations).
In another study, a number of solid tumor tissues (lung, ovarian, pancreatic) expressed ROR1 but not the normal cell counterpart. ROR1 expression was associated with high-grade histology and activation of AKT and CREB. Silencing of ROR1 using shRNA induced apoptosis of pancreatic and ovarian cancer cell lines and down regulation of the ROR1 protein as well as of activated AKT and CREB (Zhan S et al, American Journal of Pathology, 181:1903-1910, 2012).
Melanoma cells have been shown to express ROR1. ROR1 siRNA induced down regulation of ROR1 both at the mRNA and protein level, which preceded apoptosis. Targeting ROR1 of the melanoma cells by ROR1 directed monoclonal antibodies induced a significant apoptosis not requiring immune cells or complement. The degree of apoptosis induced by the antibodies varied between the cell lines (Hodjat-Farsangi M et al, PLoS One, 8, e61167, 2013).
Furthermore, it has recently been shown that ROR1 plays an important role in adipogenesis and glucose homeostasis in 3T3-L1 cells (Sanchez-Solana, B, Laborda, J and Baladron, V, Molecular Endocrinology 26: 110-127, 2012). Hence, manipulating the WNT pathway, e.g. by modulation of ROR1, to alter adipose cellular makeup may constitute an attractive drug-development target to combat obesity-associated metabolic complications (Christodoulides, C, Lagathu, C, Sethi, J K and Vidal-Puig, A, Trends Endocrinol. Metab., 2009 January; 20(1):16-24).
The above described data serve to illustrate the validity of modulating ROR1 activity for treatment of disorders and diseases that include not only chronic lymphocytic leukemia (CLL) but also other hematological malignancies as well as solid tumors and obesity-associated metabolic complications.
Antibody inhibitors of ROR1 have been described in the literature; see e.g. PCT Int. Appl. WO2011079902. There are, however, no small molecule inhibitors of ROR1 known in the art.
Substituted imidazo[4,5-b]pyridine compounds are well known in the art, see e.g. PCT Int. Appl. WO2003045929, WO2004016270, WO2004016611, WO2006066913, WO2006066914, WO2006080821, WO2006125958, WO2007028135, WO2007072017, WO2007083978, WO2008121063, WO2008121064, WO2009001021, WO2009111277, WO2011066211, WO2013116291, and Wang, T. et al. Bioorg. Med. Chem. Lett., 22(5), 2063-2069, 2012. However, it has not previously been shown that such compounds are capable of modulating ROR1 activity.